While assembling a plastic building, I decided it would look much better if the exterior lights actually worked, so I set about designing some exterior lights.
I used OpenSCAD to design a half hemispherical shade (5mm diameter) with a small wall mount. A 1mm diameter hole allows for the wiring of a surface mount 0402 LED. After three 3D printing iterations I ended up with a usable design.
I painted the inside with silver acrylic paint, and threaded an LED in to test it out.
A drop of super glue holds the light in place.
I will use these on the row of Vollmer buildings I am constructing. I will probably run two 5V power circuits to the buildings, one, always powered, for internal lights and the controller for the butcher shop and the other, switched, for night time when exterior lights are appropriate.
A 5mm light in HO scale represents a 43.5cm light - a reasonable size. I could probably make them even smaller.